Sound, 75 waves, 104, 120 Space, interstellar, 310, 313 Spectroscope, 47, 79 Spectrum analysis, 50, 139 Spiral nebulae, 322 Stars, fixed, 58 number of, 11, 306 binary, 309 distances of, 280 magnitude of, 306, 309 colour of, 79, 308 motion of, 310-11 nebulous, 320 proper motions of, 312 variable, 307 double, 308 clusters of, 314 orbits of, 310 are magnets, 307 Stokes, Sir G., 69, 152, 218 String, 21 Sun, diameter of, 280 constitution of, 79 a magnet, 164, 198-9 mass of, 190 heat of, 109 motions of, 270 orbital velocity of, 35 rotation of, 246 centre of two forces, 186 Tails of comets, 300, 304 straight, 300 curved, 301 multiple, 300 Tait, Prof., 18, 40-1, 88, 247 Telescope, 79 Temperature, 104-5 Terrestrial magnetism, 207-12 gravity, 29 Theory, atomic, 44 rules for making, 3 undulatory, 123 of exchanges, 105 Thermodynamics, first law of, 87, 114 second law of, 116 Thomson, J. J., Prof., 43, 326, 335 Tidal water-power, 88 Tides, 89, 96 Torsion balance, 185 Trade winds, 96, 249 Transformation of energy, 86 of motion, 93 Transverse vibration of light, 130 Tuning-fork, 104 Tympanum, 120 Tyndall on radiation, 104, 106 on light, 71 on Lines of Force, 174 on aether, 77 on atoms, 106 on aether waves, 112 Ultra-violet rays, 140 red rays, 140 Unity of universe, 322-9 Universal gravitation, 24 aether, 58 Universe, 313, 322, 347 Uranus, 68 mass of, 235 density of, 242 orbital velocity of, 265 a magnet, 196 Ursa Major, 307 Minor, 307 Vapour, 49 Variation, magnetic, 209-11 Velocity of light, 148 of electric waves, 182 of heat waves, 148 of falling bodies, 21 of wave motion, 76 Velocity, angular, 250 Venus, 33, 68, 79 a magnet, 197 mass of, 235 rotation of, 219 orbital velocity of, 251 periodic time of, 251 Vibration, atomic, 75 Vibrations, transverse, 130 longitudinal, 130 of sound, 123 Vibratory motion, 91 Vogel, Prof., 308, 312 Vogt, Prof., 332 Volume of sun, 27 Von Asten, 234, 296 Vortex theory, 92, 337 motion, 221-4 atom, 93, 126, 337 rings, 125, 337 Vortices, molecular, 103 Water waves, 124 currents, power of, 95 composition of, 141 power, 88 Wave front, 128 motion, 124, 160 Wave lengths, 120 envelope, 112 Waves, chemical, 141 sound, 104, 120, 124 light, 126 heat, 141 electric, 159 spherical, 112 electro-magnetic, 165 Weight, 29, 69, 84 variation of, 29 pound, 30 Whewell, 3, 221 Winds, 81, 90 energy of, 90 trade, 225 Work, 96 and energy, 84 from heat, 116 Young, Thomas, 54, 64, 67, 123 on aether, 58 fourth hypothesis, 70 Prof., of America, on electric space, 166 Zinc, 88 Zodiacal light, 277-9 _Richard Clay & Sous, Limited, London & Bungay._ Some New Publications OF Messrs. Chapman & Hall, Ltd. 1903-4